h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

Spending a day in Paris with the tour group would have been excruciating, especially since a perfume factory was on the agenda. So, the Metro offered a viable alternative. All of Paris was at the fingertips of two adventurous tourists. The first stop was the ticket booth. A book of ten tickets openned up the entire city. The Metro trains are identified by the destinations at the two ends of the route, and the maps are color coded with pretty pictures. You don't even need an electronic thumb, the Metro trains are reliable, on time, and always stop at the station.

Two additional comments:
One nice thing about Paris's Metro is it goes *everywhere*, and it's set up so you never have to make more than 2 line changes.
Also, don't stand like a chump waiting for the doors to open -- you need to *push* them open. I reminded myself of this the embarassing way, showing my mother around Paris.